Video projection system

ABSTRACT

The invention relates to a video projection system comprising at least a light source coupled to a reflector for focusing the light beam, a motor-driven color wheel having a plurality of light-transmitting segments, at least some of said segments being dichroic filters for the colors red, green, and blue, while the speed of rotation of said wheel can be modified by a control, a lens system imaging the focused light beam onto a display, a display system comprising at least a display and a display control, and a projection lens, wherein the video projection system has a video projection mode and a lighting mode, and in addition the color wheel is stationary in the lighting mode and at least one segment of the color wheel can be given a defined position in the beam.

The invention relates to a video projection system comprising at least alight source which is coupled to a reflector for forming the light intoa beam, a motor-driven color wheel which has several segments, at leastsome of said segments being dichroic filters for the colors red, green,and blue, and whose speed of rotation can be controllably changed by acontrol, a lens system which pictures the focused light beam on adisplay, a display system at least comprising a display and a displaycontrol, and a projection lens.

Video projection systems have a construction which is geared inparticular to the requirements of the display or displays used.

Video projection systems with several displays, in particular with threedisplays, and with dichroic filters distinguish themselves by a highefficiency, but they require a high financial investment. This is causedin particular by the expense necessary for the three displays, thehigh-technology optical system, and the intricate mounting andpixel-critical adjustment of the projection system.

In addition, less expensive projection systems with only a singledisplay are available. These systems usually have a comparatively simpleoptical system and generate colors sequentially in time in thatconsecutively a red, a blue, and a green picture are projected. Adisadvantage of this projection system is that approximately two thirdsof the available quantity of light cannot be utilized owing to the verynature of the method, because only one of the three colors can be usedfor projection at any given moment. Since this detracts in particularfrom the brightness of so-termed “white scenes”, a certain proportion ofwhite light is transmitted in addition to the three color sequences.

The light beam generated by a conventional light source is often used ina video projection system of the above type in conjunction with areflector and/or a convergent lens. This focused light beam then hits arotating color wheel positioned in the path of the beam, which wheelgenerates the three color sequences. The color wheel rotates in aregular rotation driven by an electric motor at a speed of approximately3600 to 7200 rpm. The speed of the color change thus generated isregulated and synchronized by the display control. The speed of thecolor wheel can be changed by a conventional control, for examplecontinuously, if so desired. The speed change of the color wheel takesplace in that the color change is synchronized in a usual manner withthe image frequency, for example 50 to 60 Hz.

The color wheel has a plurality of segments which are arranged next toone another along the circumference of the color wheel and which enterthe light beam one after the other owing to the rotation of the colorwheel. Said segments are, for example, dichroic filters for red, green,and blue. If a proportion of “white light” is to be projected inaddition, at least one transparent segment is arranged on the colorwheel in the same manner.

A lens system which images the focused light beam on the display is thenext component arranged in the path of the beam of the video projectionsystem. Apart from the display, the display system comprises at least adisplay control which realizes inter alia the synchronization of thespeed of the color wheel with the image frequency. The light beamleaving the display is incident on a conventional projection lens, sothat a projection of moving shapes or videos is realized visible to thehuman eye. A light source of high luminous intensity is mostly used forvideo projection systems complying with high optical requirements. Lamptypes that can be used for video projection in this respect are, forexample, short-arc metal halide gas discharge lamps, xenon high-pressurelamps, and increasingly UHP (ultra high performance) lamps.

Inexpensive projection systems with rotating color wheels and only asingle display can in principle be operated not only in an operationalvideo projection mode but also in a lighting mode, i.e. a light beam isemitted for lighting purposes, for example as with a conventionalspotlight. If a conventional color-sequence video projection system isto be used for illumination with red light, the display is to beswitched to “dark” with respect to the green and blue, and possibly thewhite sequences, so that these sequences do not contribute to theillumination. In this lighting mode, color-sequence video projectionsystems do not achieve the brightness of a spotlight having a comparablelight source.

In addition, spotlights are known for fulfilling high requirements inthe fields of stage, sports, and disco lighting. More recent spotlightstend to resemble the described video projection systems as regards theirtechnical construction, for example the electronic control of themotors, the color wheels, diaphragm and lens systems, and theirapplication, for example the projection of still images. Such aspotlight is known from U.S. Pat. No. 6,113,252. The spotlight describedtherein has a lamp as its light source. The light of this lamp is formedinto a beam by a reflector, is homogenized by a multiple-lensintegrator, and is used for illuminating a diaphragm which is imaged onthe scene to be illuminated. Said diaphragm can be regularly exchangedby a motor and may have special shapes, for example generating stillimages. Multi-color wheels are arranged in the path of the beam, capableof generating any mixed colors desired, depending on their position. Toenlarge the color space that can be displayed, several such color wheelsare positioned one after the other in the beam path. The projection ofmoving images and videos is not possible with the known spotlights.

It is an object of the invention to provide a video projection systemwith a display which in its lighting mode has the properties of aspotlight with a comparable light source, in particular as regards thebrightness of the radiated light, and which operates efficiently.

The object of the invention is achieved in that the color wheel isstationary in the lighting mode, at least one segment of the color wheelcan be given a defined position in the beam path, and the display can beswitched at least partly to “bright” by the display control.

The rotating color wheel is brought to a standstill upon the transitionfrom the video projection mode to the lighting mode. The definedpositioning of the color wheel in the beam path may be realized in thecourse of decelerating and stopping of the color wheel or starting fromthe stationary position. In the technically simplest case, this requiresmerely a change in the control of the motor in combination withconventional methods and/or known devices for positioning a wheel drivenby a shaft.

The solution according to the invention provides a video projectionsystem with only one display which in its operational functions combinesthe primary properties of a conventional projection system in the videoprojection mode with those of a fully fledged spotlight in the lightingmode. The multifunctional applications in the video projection andlighting modes of the new system thus achieved enable in particular theprofessional users to achieve the known advantages of so-termed“combination devices” such as, for example, a reduced investment andmaintenance cost compared with the two systems necessary until now forachieving the same functions and quality, without a significantreduction in performance having to be taken into the bargain.

A defined positioning of the color wheel or at least of a segment in thebeam will always be such within the scope of the invention that at leastpart of the light beam passes through the color wheel in its beam.

Displays within the scope of the invention are all known electronicdisplays that can be used at present for video projection. Thesedisplays render possible two switching modes, i.e. “bright”, i.e. lightmay pass through, and “dark”, i.e. no light can pass through. They mayalso represent continuous grey levels. The displays are, for example,sequential LCDs (Liquid Crystal Displays) or a DMD (Digital MicromirrorDevice) system from the company of Texas Instruments Inc., which areparticularly suitable for use of the video projection systems accordingto the invention in the higher luminous flux ranges.

Display systems comprise besides the displays as their core elements allknown components and interfaces known in this connection which arenecessary for satisfactory operation and external and/or internalcommunication, for example for synchronizing the color wheel speed withthe image frequency.

Light sources capable of providing high luminous fluxes are inparticular xenon high-pressure lamps and increasingly UHP (ultra highperformance) lamps (DE 38 134 21). UHP lamps can operate with arclengths below 2 mm and as a result have a very high efficiency inoptical systems. Apart from fulfilling the brightness criterion and thatof being as point-shaped a light source as possible, this lamp typeprovides the properties aimed at in video projection systems, i.e. agood spectral light distribution and constancy of properties throughoutthe entire, long lamp life.

The invention is advantageously embodied in, inter alia, a video systemwhich displays a sequence of images when it is in the lighting mode aswell as the other, further embodiments of the invention set forthherein.

A further advantageous embodiment of the invention relates to thegeneration of desired mixed colors, for which the color wheel can bepositioned in the lighting mode in such a manner that the focused lightbeam is incident on two dichroic filters of the color wheel. Positioningof the color wheel, and thus of a portion of the color wheel in the beamin the manner indicated above causes the light beam to be incident ontwo mutually adjoining dichroic filters of the color wheel, whereby amixed color is generated.

The general color theory teaches that mixing of the so-termed chromaticcolors red, green, and blue leads to the known mixed colors, in contrastto non-chromatic such as white, grey, and black. The chrominance is thecharacteristic of all chromatic colors. The degree to which thechrominance prevails determines the saturation of a chromatic color.Each color has a brightness. Each color can be measured andunequivocally described by means of these three characteristics.

It is furthermore preferred that the color wheel used has at least onetransparent segment in addition to the red, green, and blue segments.The known advantages can be achieved thereby in the video projectionmode. If the focused light beam is exclusively incident on a transparentsegment in the lighting mode, only “white light” will be projected.Colors of different saturation can be generated in that the light beamis incident on a transparent segment and a dichroic filter.

Particularly advantageous is the use of a color wheel having eightsegments, six of these segments being dichroic filters for the colorsred, green, and blue, and two segments being transparent, which eightsegments are arranged immediately next to one another over thecircumference of the color wheel in the sequence: red, green, blue,transparent, green, red, blue, transparent. This irregular arrangementof the eight segments, in which each segment occurs twice, increases thenumber of mixed colors and colors of different saturation that can begenerated in a simple manner. The display control must take into accountthis sequence of the eight segments in an appropriate manner in thevideo projection mode.

The following embodiments of the invention are regarded as preferred,alternatively or jointly, for achieving a defined positioning of thecolor wheel: a detection arrangement, an electronically commutatedmotor, and/or sensors for color measurement.

Such a detection arrangement (“photoelectric barrier”) senses the marksprovided on the color wheel outside the portions of the color wheelutilized for the passage of the light beam. The position of the colorwheel is changed on the basis of a simple control loop until the signaldetected by the photoelectric barrier corresponds to the given requiredvalue. In the simplest case, marks of different sizes in the positionscorresponding to the respective colors will suffice.

The use of an electronically commutated motor as a drive renders a veryaccurate positioning possible on account of its control. An associatedcircuit converts the required value, corresponding to the respectivecolor, into the required motor position. In addition, three sensorssensitive to the primary colors can measure the actual color value ofthe generated light beam. A feedback circuit which has access to thestored data of the color structure of the respective color wheel movesthe color wheel until the desired color has been adjusted.

The degree of homogeneity of the focused light beam may be improved byarranging an integrating rod in the beam between the color wheel and thelens system. This arrangement is particularly effective in thegeneration of mixed colors. Multiple internal reflections mix the inputlight beam such that a homogeneous illumination with the mixed color isachieved at the output side of the integrating rod.

The use of a color wheel on which a lithographically structured,dichroic filter is arranged is also preferred. The filters aremechanically interconnected on the color wheels widely used nowadays, sothat their interconnection locations often have edges which mayinterfere with the desired beam. Such interferences can be eliminated tothe highest degree possible by means of a lithographically structured,dichroic filter which may be arranged, for example, on a highlyheat-resistant glass (hard glass). A filter of the type described alsocontributes to as little light as possible being absorbed in thelighting mode.

If it should be possible to display all colors or mixed colorsobtainable on the basis of the colors red, blue, and green, it ispreferred that a total number of dichroic filters for red, green, andblue is arranged on one color wheel or on several color wheels such thateach of these three colors is arranged directly next to one of the twoother colors at least once, and in addition each of these three colorsis arranged next to a transparent segment at least once.

The provision of a second color wheel or further color wheels in thebeam renders it possible to widen the range of obtainable colors, i.e.mixed colors, further.

The invention will be explained in more detail below with reference toan embodiment, as shown in the drawings, in which:

FIG. 1 shows the arrangement of segments on a color wheel; and

FIG. 2 is a diagram of an exemplary video projection system.

The video projection systems according to the invention with only onedisplay can be operated with a high efficiency both in the video modeand in the lighting mode. The video projection system has a known,comparatively simple optical system which renders it possible to projectthe colors generated in a time sequence one after the other. The lightbeam generated by a conventional light source, for example a UHP lamp,is focused by a reflector in the video projection system. This focusedlight beam then hits a rotating color wheel 1 in FIG. 1 which isarranged in the beam and which generates in particular the three colorsequences. The color wheel 1 is driven into rotation by an electricmotor with a speed of approximately 3600 to 7200 rpm, but alternativespeed ranges may also be possible. The speed of the color change thusgenerated and the sequence of the eight segments 2 on the color wheel 1are synchronized by the display control. The speed of the color wheel 1is adapted by a conventional, continuous control of the image frequency.

FIG. 1 diagrammatically shows the arrangement of the segments 2 on thecolor wheel 1, which has eight segments 2 which are distributed next toone another over the circumference of the color wheel 1 and which enterthe beam one by one owing to the rotation of the color wheel 1. Sixsegments 2 are dichroic filters for red R, green G, and blue B. Twotransparent segments 2 are arranged on the color wheel 1 for projecting“white light”. The sequence of the colors that can be generated is inclockwise direction: red R, green G, blue B, “white” W, green G, red R,blue B, and “white” W.

FIG. 2 diagrammatically shows an arrangement of a video projectionsystem The light beam generated by a light source 5 is focused by areflector 6 in the video projection system 3. The degree ofhomogenization of the focused light beam is improved through thearrangement of an integrating rod 7 in the beam between the color wheel1 and a lens system 4. Multiple internal reflections mix the input lightbeam such that a homogeneous illumination is obtained at the output sideof the integrating rod 7. Downstream thereof, the lens system 4 isarranged in the beam of the video projection system 3, imaging thefocused light beam onto the DMD display 8. The lens system 3 maycomprise lens(es), prism(s) and other components, as it known to one ofordinary skill in the art. The display system comprises besides thedisplay 8 at least a display control 9 which realizes, inter alia, thesynchronization of the color change with the image frequency. Thedisplay control 9 here gives a signal 10 which leads to thesynchronization of the speed of the motor (11)-driven color wheel 1. Alamp power supply 14 is connected to the lamp 5 and to the displaycontrol 9. The lamp power supply 14 feeds power to the lamp 5synchronized with the display 8 and the color wheel 1, as is known toone of ordinary skill in the art. The light beam leaving the display 8is incident on a conventional projection lens 12, so that a projectionof moving shapes or videos visible to the human eye is realized. Theprojection systems with rotating color wheels and only a single display,which are inexpensive compared with a system having three displays, maybe operated as effectively in the lighting mode, for example as aconventional spotlight. If the color-sequence video projection system isto be used for illumination with red light, the display is to beswitched correspondingly, and the color wheel is to be held stationaryin a position such that the focused light beam is incident only on adichroic filter for the color red. While the present invention has beendescribed in particular detail with reference to specific exemplaryembodiments thereof, it should also be appreciated that, as is known toone of skill in the art, numerous modifications and changes may be madethereto without departing from the broader and intended spirit and scopeof the invention as set forth in the claims that follow. Thespecification and drawings are accordingly to be regarded in anillustrative manner and are not intended to limit the scope of theappended claims.

If a certain shape is to be illuminated, for example, or a textcharacter or a sample, also denoted “gobo”, is to be represented in acertain color, the shape to be illuminated is shown on the display, andthe color chosen for the illumination is adjusted in that the colorwheel is positioned.

In this operating mode, accordingly, the video projection systemachieves a brightness comparable to that of a spotlight having a lightsource of the same strength.

1. A video projection system comprising at least a light source coupledto a reflector configured to concentrate the light into a beam, amotor-driven color wheel positioned to receive the beam, themotor-driven color wheel having plurality of light-transmittingsegments, at least some of said segments being dichroic filters for thecolors red, green, and blue, the color wheel being rotatable and havinga rotation modifiable by a control, a lens system configured to imagesthe beam onto a display, a display system comprising at least thedisplay and a display control, and a projection lens positioned toreceive the beam from the display, wherein said video projection systemhas not only a video projection mode but also a lighting mode, andwherein the video projection system comprises means for rendering thecolor wheel stationary with at least one segment of the color wheel at adefined position in the beam path, when the video projection system isin the lighting mode.
 2. The video projection system of claim 1, whereinthe display is configured to display a sequence of images on the displaywhen the video projection system is in the lighting mode.
 3. The videoprojection system of claim 1, wherein the color wheel can be positionedin the lighting mode such that the beam from the reflector is incidenton one or on two dichroic filters of the color wheel.
 4. The videoprojection system of claim 1, wherein the color wheel has at least oneclear colorless segment.
 5. The video projection system of claim 1,wherein the color wheel has eight segments, of which six segments aredichroic filters for red (R), green (G), and blue (B), and two segmentsare clear colorless (W), which eight segments are arranged directly nextto one another along the circumference of the color wheel in thesequence: red (R), green (G), blue (B), transparent (W), green (G), red(R), blue (B), and transparent (W).
 6. The video projection system ofclaim 1, wherein the means for rendering the color wheel stationarycomprises at least one of a detection arrangement, an electronicallycommutated motor, or sensors for color measurement.
 7. The videoprojection system of claim 1, wherein an integrating rod is arranged inthe beam between the color wheel and the lens system.
 8. The videoprojection system of claim 1, wherein a lithographically structureddichroic filter is arranged on the color wheel.
 9. The video projectionsystem of claim 1, wherein at least a second color wheel is positionedin the beam.
 10. The video projection system of claim 1, whereindichroic filters for red, green, and blue are arranged on one colorwheel or on several color wheels such that overall each of these threecolors is arranged directly next to one of the two other colors at leastonce, and each of theee three colors is arranged next to a transparentsegment at least once.
 11. The video projection system of claim 1,wherein the projection system is configured for as a spotlight.
 12. Avideo projection system comprising at least a light source coupled tomeans for concentrating light from the light source into a beam, amotor-driven color wheel positioned to receive the beam, themotor-driven color wheel having a plurality of light-transmittingsegments, at least some of said segments being dichroic filters forcolors, the color wheel being rotatable and having a rotation modifiableby a control, a lens system configured to image the beam onto a display,a display system comprising at least the display and a display control,and a projection lens positioned to receive the beam from the display,wherein said video projection system has not only a video projectionmode but also a lighting mode, and wherein the video projection systemcomprises means for rendering the color wheel stationary with at leastone segment of the color wheel) at a defined position in the beam path,when the video projection system is in the lighting mode.
 13. The videoprojection system of claim 12, wherein the means for concentrating lightis a reflector.
 14. The video projection system of claim 12, wherein themeans for concentrating light is a convergent lens.